[LEDE-DEV] [PATCH ubox] getrandom: add helper for getrandom() syscall

[John Crispin]

Hi Etienne,

pushed the patch to ubox.git and updated the ubox package inside my
staging tree. should the tool be installed to /usr/bin ? if not let me
know and i will fix the staged commit.

	John

On 09/06/2016 15:03, Etienne CHAMPETIER wrote:
> getrandom() was introduced in version 3.17 of the Linux kernel.
> By default getrandom() block until /dev/urandom pool has been initialized
> and then read from it.
> Read buffer is 256 bytes so getrandom() calls always succeed.
> 
> First usage will be to save a seed for /dev/urandom.
> 
> Signed-off-by: Etienne CHAMPETIER <champetier.etienne at gmail.com>
> ---
>  CMakeLists.txt |  5 +++++
>  getrandom.c    | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 63 insertions(+)
>  create mode 100644 getrandom.c
> 
> diff --git a/CMakeLists.txt b/CMakeLists.txt
> index 834b5b6..73e8753 100644
> --- a/CMakeLists.txt
> +++ b/CMakeLists.txt
> @@ -16,6 +16,11 @@ IF(DEBUG)
>    ADD_DEFINITIONS(-DDEBUG -g3)
>  ENDIF()
>  
> +ADD_EXECUTABLE(getrandom getrandom.c)
> +INSTALL(TARGETS getrandom
> +	RUNTIME DESTINATION bin
> +)
> +
>  ADD_EXECUTABLE(kmodloader kmodloader.c)
>  TARGET_LINK_LIBRARIES(kmodloader ubox)
>  
> diff --git a/getrandom.c b/getrandom.c
> new file mode 100644
> index 0000000..9671202
> --- /dev/null
> +++ b/getrandom.c
> @@ -0,0 +1,58 @@
> +/*
> + * Copyright (C) 2016 Etienne Champetier <champetier.etienne at gmail.com>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +#define _GNU_SOURCE
> +#include <errno.h>
> +#include <linux/random.h>
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <sys/syscall.h>
> +#include <unistd.h>
> +
> +#define ERROR_EXIT(fmt, ...) do { \
> +        fprintf(stderr, fmt, ## __VA_ARGS__); \
> +        return EXIT_FAILURE; \
> +        } while (0)
> +
> +static int usage(char *name)
> +{
> +    fprintf(stderr, "Usage: %s <nb>\n", name);
> +    fprintf(stderr, " => return <nb> bytes from getrandom()\n");
> +    return EXIT_FAILURE;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> +    if (argc != 2)
> +        return usage(argv[0]);
> +
> +    if (isatty(STDOUT_FILENO))
> +        ERROR_EXIT("Not outputting random to a tty\n");
> +
> +    int nbtot = atoi(argv[1]);
> +    if (nbtot < 1)
> +        ERROR_EXIT("Invalid <nb> param (must be > 0)\n");
> +
> +    char buf[256];
> +    int len = sizeof(buf);
> +    while (nbtot > 0) {
> +        if (nbtot <= sizeof(buf))
> +            len = nbtot;
> +        if (syscall(SYS_getrandom, buf, len, 0) == -1)
> +            ERROR_EXIT("getrandom() failed: %s\n", strerror(errno));
> +        if (write(STDOUT_FILENO, buf, len) != len)
> +            ERROR_EXIT("write() failed: %s\n", strerror(errno));
> +        nbtot -= sizeof(buf);
> +    }
> +}
>